It is the goal of this study to define the role of the respiratory epithelium of the lung in the maintenance of fluid distribution across the barrier between blood and air. Several preparations, including the excised amphibian lung, the perfused, fluid-filled rat lung lobe, the in vitro rat trachea, canine airways in vitro, and an oil blocked, microlavaged terminal alveolar sac of the rat lung, will be examined. These preparations either restrict solute transfer to paths across the alveolar epithelium (excluding parallel routes through airway epithelium) or permit estimation of alveolar permeability from the difference between measurements from the whole lung lobe and the trachea and bronchi. The proposed studies with amphibian lung will extend our earlier work by examining nonelectrolyte, K ion, and Ca ions fluxes along with the effcts of two groups of environmental pollutants (heavy metals, and the dipyridilium herbicides) on bioelectric properties, solute permeability, and tissue composition. Micropuncture and oil blockade of a terminal alveolar sac will allow measurment of the transalveolar bioelectric p.d. and solute permeability. Each result will be compared with the values for the alveolar epithelium that are predicted by difference from similar measurements on whole lobe and airways. Effects of the selected pollutants on these parameters will be explored. Thus, a second objective of this project is to identify the locus and nature of pollutant damage to the air-blood barrier and to relate this damage to metabolic events in the epithelium.